1. Field of the Invention
The present invention relates to a steering wheel to be mounted on a vehicle, and, more particularly, to a steering wheel having an impact energy absorbing member included in a pad which is fastened to the upper surface of the boss portion of the steering wheel.
2. Description of the Prior Art
Hitherto, there has been disclosed a steering wheel arranged in such a manner that an impact energy absorbing member made of sheet metal is disposed in a box-like pad which is fastened to the upper surface of the boss portion of the steering wheel whereby impact energy acting on the pad can be absorbed (see Japanese Utility Model Unexamined Publication No. 58-143766).
Since the above-disclosed steering wheel is arranged in such a manner that the pad is mainly made of a soft synthetic resin, a pipe-like insert made of a semi-rigid synthetic resin is embedded in the pad for the purpose of retaining the outer shape of the pad. Furthermore, the energy absorbing member made of sheet metal and having an n-shape cross section is disposed in the above-described pad. The pad with the energy absorbing member thus-disposed is fastened to the upper surface of the boss portion of the steering wheel body.
In a state where the above-described steering wheel is fastened to the steering shaft, the upper wall of the pad is downward inclined in the forward direction of the vehicle so that the meter visibility is improved. Also the upper wall of the energy absorbing member is downward inclined in the same direction in such a manner that it runs substantially parallel to the upper wall of the pad.
However, if the upper wall portion of the pad of the conventional steering wheel thus-constituted is inclined in order to further improve the above-described meter visibility, the upper wall of the energy absorbing member necessarily is inclined considerably. Therefore, problem arises in that, when an impact force from an upper portion acts in a downward direction on the central portion of the upper wall portion of the pad, the component of the force pressing the energy absorbing member rearward is enlarged excessively and thereby the side wall portion of the energy absorbing member cannot be deformed so as to be sufficiently crushed.
Furthermore, it might be considered feasible to employ a structure arranged in such a manner that the costly soft synthetic resin such as the urethane resin employed to manufacture the pad is replaced by a relatively cheap rigid synthetic resin such as polypropylene to reduce cost. In this case, the major portion of the pad, which defines the shape of the pad, is made of the thus-employed rigid synthetic resin and the surface of the pad is covered with a cover layer made of the soft synthetic resin so that the overall cost required to manufacture the pad can be reduced. However, if the pad of the conventional steering wheel is made of the rigid synthetic resin, there arises a problem in that the side wall portion of the box-like pad cannot be easily deformed due to the rigidity of the employed rigid synthetic resin and thereby there is a fear that the side wall portion of the energy absorbing member cannot sufficiently be deformed.
A structure has been disclosed in Japanese Utility Model Unexamined Publication No. 62-194177 which is arranged in such a manner that a pad having a reverse side, to which a metal member for fastening the impact energy absorbing member or the like is secured, is fastened to the steering wheel body.
According to the above-disclosed structure for fastening the pad to the steering wheel body, the impact energy absorbing member comprises a deformable portion which absorbs impact energy when it is deformed and which has an inverted U-shaped cross section and a substantially rectangular frame-like base portion to be secured to the above-described deformable portion, both the deformable portion and the base portion being made of sheet metal. Furthermore, a plurality of fitting legs made of rigid synthetic resin are screwed to the base portion. On the other hand, the steering wheel body has, in a boss plate thereof, a plurality of fitting holes which correspond to the above-described fitting legs, the boss plate constituting the metal core of the steering wheel.
By inserting each of the fitting legs into the fitting hole until the fitting legs are engaged to the peripheral portions of the fitting holes, the pad can be fastened to the steering wheel body.
However, since the above-described conventional structure for fastening the pad to the steering wheel body is arranged in such a manner that the fitting legs are screwed to the base portion of the impact energy absorbing member, the number of parts cannot be reduced, causing the number of manufacturing processes to be increased when the steering wheel arranged in such a manner that the pad having the impact energy absorbing member is fastened to the steering wheel body is manufactured.
In addition, a structure, in which a horn pad is fastened to a fixed contact plate, has been disclosed in Japanese Utility Model Unexamined Publication No. 63-172774.
According to the above-disclosed structure, a horn switch mechanism composed of a movable contact plate made of a leaf spring and a fixed contact plate made of sheet metal is disposed on the reverse side of the horn pad. The horn pad is fastened to the fixed contact plate in such a manner that the horn pad is able to move to approach the above-described fixed contact plate by the above-described movable contact plate made of the leaf spring and thereby serving as an urging member. Furthermore, the horn pad is fastened to the fixed contact plate in such a manner that it is urged so as to be positioned away from the fixed contact plate by a predetermined distance.
Specifically, the horn pad is fastened to the fixed contact plate in such a manner that substantially-cylindrical spacers, each of which has a flange portion at an end portion thereof and which are made of synthetic resin, are respectively inserted into a plurality of fastening holes formed in the fixed contact plate in such a manner that the other end portion of each of the spacers faces the horn pad. Then, each of the flange portions is brought into contact with the peripheral portion of each of the fastening holes before each of the spacers is screwed to the reverse side of the horn pad. As a result, the fixed contact plate is fastened to the reverse side of the horn pad.
The movable contact plate is disposed between the fixed contact plate and the horn pad in such a manner that its contact portion is disposed on the reverse side of the horn pad so as to urge the horn pad to move away from the fixed contact plate. The distance of the movement away from the fixed contact plate is restricted by the fact that the flange portion of the spacer screwed to the horn pad comes in contact with the peripheral portion of the fastening hole formed in the fixed contact plate.
When the horn switch is operated, the horn pad is depressed so that its contact portion is moved downward to come in contact with the fixed contact plate because the horn pad is, on the reverse side thereof, supported by the contact portion of the movable contact plate. As a result, the horn is operated. At this time, the horn pad approaches the fixed contact plate by the action of the spacer which slides on the inner surface of the fastening hole formed in the fixed contact plate and which serves as a guide member for guiding the horn pad.
The above-described spacer is provided for the main purpose of preventing undesirable contact which will take place between the fixed contact plate and the above-described fastening screw.
However, the conventional structure for fastening the horn pad to the fixed contact plate must use a plurality of fastening screws and the spacers of the same number must be placed at the fastening portions.
As described above, since a large number of screws and spacers must be used in the conventional fastening structure, the number of parts for use at the time of the fastening process cannot be reduced, causing a considerable number of fastening processes. As a result, the fastening cost cannot be reduced.